Hello, Jan.

On Mon, Nov 28, 2016 at 11:07:18AM +0100, Jan Kara wrote:

As I'm looking into the code, we need a serialization between bdev writeback
and blkdev_put(). That should be doable if we use writeback_single_inode()
for writing bdev inode instead of simple filemap_fdatawrite() and then use
inode_wait_for_writeback() in blkdev_put() but it needs some careful
thought.

It's kinda weird that sync() is ends up accessing bdev's without any
synchronization.  Can't we just make iterate_bdevs() grab bd_mutex and
verify bd_disk isn't NULL before calling into the callback?

Frankly that whole idea of tearing block devices down on last close is a
major headache and keeps biting us. I'm wondering whether it is still worth
it these days...

Yeah, it'd be great if we can follow a more conventional lifetime
pattern here.

Thanks.

-- 
tejun

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